In underground drilling, such as gas, oil or geothermal drilling, a bore hole is drilled through a formation in the earth. Bore holes are formed by connecting a drill bit to sections of long pipe so as to form an assembly commonly referred to as a “drill string” that extends from the surface to the bottom of the bore. The drill bit is rotated so that it advances into the earth, thereby forming the bore. A high pressure drilling fluid, typically referred to as “drilling mud” is pumped down through the drill string to the drill bit so as to lubricate the drill bit and to flush cuttings from its path. The drilling fluid then flows to the surface through the annular passage formed between the drill string and the surface of the bore hole.
Downhole measuring and communication systems frequently referred to as measurement-while-drilling (“MWD”) and logging-while drilling (“LWD”) are typically disposed within drill string sections above and in close proximity to the drill bit. The systems comprise sensors for collecting downhole parameters, such as parameters concerning the drilling assembly itself, the drilling fluid, and those of formations surrounding the drilling assembly. For example, sensors may be employed to measure the location and orientation of the drill bit, and to detect buried utilities and other objects—critical information in the underground utility construction industry. Sensors may be provided to determine the density, viscosity, flow rate, pressure and temperature of the drilling fluid. Other sensors are used to determine the electrical, mechanical, acoustic and nuclear properties of the subsurface formations being drilled. Chemical detection sensors may be employed for detecting the presence of gas. These measuring and communication systems may further comprise power supplies and microprocessors that are capable of manipulating raw data measured by the various sensors. Information collected by sensors may be stored for later retrieval, transmitted to the earth's surface via telemetry while drilling, or both. Transmitted information provides the bases for adjusting the drilling fluid properties and/or drilling operation variables, such as drill bit speed and direction.
A mule shoe mounted within a drill string section may be used as a seat for components associated with MWD/LWD systems. Although the mule shoe helps to positively secure seated components in both a radial direction and a circumferential direction, gravity and drilling fluid are the only forces acting on the components to maintain their axial (or vertical) position. Movement of a MWD/LWD component in the vertical direction is desired such that the component can be retrieved from a downhole position, in the event of failure for example, without having to retract the entire drill string section from the bore hole.
Vertical movement of a MWD/LWD component is not however without several disadvantages. First, as the drill bit cuts through the earth, vibrations occur and are transmitted along the drilling string. These vibrations may cause fatigue, deterioration, and finally failure of the components. Second, vertical movement of the component within a mule shoe may produce undesirable wear. Third, important positional data of the drill bit and other drill string components can be comprised with a moving reference point accompanying a MWD/LWD component.
Accordingly, there is room for improvement in the art.